A conventionally known solid polymer electrolyte fuel cell is formed from a plate-shaped electrode structure and first and second separators that sandwich the electrode structure. The electrode structure has a solid polymer electrolyte membrane, first and second electrode layers that sandwich the solid polymer electrolyte membrane, and first and second diffusion layers, which are disposed outside the corresponding electrode layers. The first separator forms, in cooperation with a face on the first diffusion layer side of the electrode structure, a first gas passage through which one type of gas among a fuel gas and an oxidizing gas flows, and the second separator forms, in cooperation with a face on the second diffusion layer side of the electrode structure, a second gas passage through which the other type of gas among the fuel gas and the oxidizing gas flows. In this case, the solid polymer electrolyte membrane, the first and second electrode layer, and the first and second diffusion layers are formed so as to have substantially the same dimensions (ref., e.g. U.S. Pat. No. 5,176,966).
However, in accordance with the above-mentioned arrangement, there might be the problem that, since outer edges of the first electrode layer and the first diffusion layer are present in the proximity of outer edges of the second electrode layer and the second diffusion layer with the outer edge of the solid polymer electrolyte membrane held therebetween, if a fuel gas and an oxidizing gas leak from the first electrode layer side and the second electrode layer side, they react with each other around the electrode structure.